Dynamic DNS Script I used for Google Domains with DD-WRT

README.md

DD-WRT Dynamic DNS for Google Domains

Create a Synthetic Record for Dynamic DNS. Copy the script and substitute your synthetic record's username, password, and FQDN in the config section.

Go to Administration > Commands tab and paste the code into the Command box, then click Save Custom Script.

Go to Administration > Management tab. Scroll down to the Cron section, and toggle Cron: Enable

In the Additional Cron Scripts section, put:

17 * * * * root /tmp/custom.sh

Scroll to the bottom. Click Apply Settings. Wait for the page to reload. Scroll back to the bottom and click Reboot Router.

Notes

• The actual call to Google's API to update your IP address will not be made unless it has changed.
• The cron timing I supplied above runs this at the 17th minute of every hour (e.g. 12:17, 1:17, etc).
  • You can run it at a different frequency by crafting a different schedule.

custom.sh

#!/bin/sh -e

### CONFIG
DDNS_USERNAME="your-dynamic-domain-username"
DDNS_PASSWORD="your-dynamic-domain-password"
DDNS_HOSTNAME="your.dynamic.domain"
### END CONFIG

# Quit if we're not up very long
UPTIME=$(cat /proc/uptime | cut -f1 -d.)
if [ "$UPTIME" -lt "180" ]; then
  exit 0
fi

# Get my public IP
PUBLIC_IP=$(ip route get 8.8.8.8 | grep -Eo 'src .*' | grep -Eo '(\d{1,3}\.){3}\d{1,3}')

# Resolve IP for DDNS record
DNS_IP=$( nslookup $DDNS_HOSTNAME | grep -Eo '(\d{1,3}\.){3}\d{1,3}' )

if [ "$DNS_IP" != "$PUBLIC_IP" ] ; then
    URL="https://${DDNS_USERNAME}:${DDNS_PASSWORD}@domains.google.com/nic/update?hostname=${DDNS_HOSTNAME}"
    wget -O - $URL 2> /dev/null
fi